Technical Field
The present invention relates to catalysts for oxidative dehydrogenation of hydrocarbons in a fluidized bed reactor. More specifically, the present invention relates to fluidizable, vanadium-based catalysts for oxidative dehydrogenation of alkanes.
Description of the Related Art
The “background” description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description which may not otherwise qualify as prior art at the time of filing, are neither expressly or impliedly admitted as prior art against the present invention.
Ethylene is a valuable feedstock for the petrochemical industry. It is used as a starting chemical to produce a wide range of chemicals and products [S. A. Mulla, O. V Buyevskaya, and M. Baerns, “A comparative study on non-catalytic and catalytic oxidative dehydrogenation of ethane to ethylene,” vol. 226, pp. 73-78, 2002—incorporated herein by reference in its entirety]. Steam cracking of petroleum hydrocarbons is the conventional source of ethylene. Steam cracking processes are energy intensive, which contribute to the high ethylene production cost. The use of petroleum feedstocks is also a main source of energy in steam cracking, making it and even more costly approach for producing ethylene. On the other hand, oxidative dehydrogenation (ODH) has the potential to produce ethylene from relatively cheaper gaseous feedstocks such as natural gas and refinery gas. The use of a suitable catalyst can efficiently process the gaseous feeds to produce ethylene.
Due to its potential, in recent years, ODH research has received a great deal of attention, both in the industrial and academic settings. As a result, the development of a suitable catalyst, that maximizes the ethylene selectivity, and minimizes the carbon dioxide formation, is most relevant for the successful implementation of the ODH of ethane technology. Keeping this in mind, most of the research reported in the literature has been focused on different aspects of ODH catalysts, such as catalyst active phases, structure or morphology which are responsible for catalyst performance.
Like other conventional heterogeneous catalytic reactions, both the support and the active metal components play important roles in ODH reactions. The most commonly studied metals are V and Cr, using different types of support materials [M. Loukah, J. C. Vedrine, and M. Ziyad, “Oxidative dehydrogenation of ethane on V- and Cr-based phosphate catalysts,” vol. 4, 1995—incorporated herein by reference in its entirety]. For example, the phosphate-supported V catalysts are more active and provide better ethylene selectivity than those which are reported for (VO)2 P2O7 [P. Ciambelli, P. Galli, L. Lisi, M. A. Massucci, P. Patrono, R. Pirone, G. Ruoppolo, and G. Russo, “TiO2 supported vanadyl phosphate as catalyst for oxidative dehydrogenation of ethane to ethylene,” vol. 203, pp. 133-142, 2000—incorporated herein by reference in its entirety]. For a Cr-containing catalyst, it was shown that at comparable conversion levels, the ethylene selectivity varied according to different supports used: (VO)2P2O7>CrPO4>Cr/α-ZrP>Cr/β-ZrP. Iron phosphate phases such as FePO4, Fe2P2O7, α-Fe3(P2O7) and β-Fe3(P2O7), and non-stoichiometric (mixed) iron phosphate phases with P:Fe ratios of 1.2:1 and 2:1 have been also reported to be active for ODH reactions [J. E. Miller, M. M. Gonzales, L. Evans, A. G. Sault, C. Zhang, R. Rao, G. Whitwell, A. Maiti, and D. King-Smith, “Oxidative dehydrogenation of ethane over iron phosphate catalysts,” Appl. Catal. A Gen., vol. 231, no. 1-2, pp. 281-292, May 2002—incorporated herein by reference in its entirety]. The nickel based Ni—Co/Al2O3 catalysts however, are shown to be active but to display low ethylene selectivity (less than 30%) [J. P. Bortolozzi, L. B. Gutierrez, and M. a. Ulla, “Synthesis of Ni/Al2O3 and Ni—Co/Al2O3 coatings onto AISI 314 foams and their catalytic application for the oxidative dehydrogenation of ethane,” Appl. Catal. A Gen., vol. 452, pp. 179-188, February 2013—incorporated herein by reference in its entirety].
Several studies investigated different acidic SAPO-34 based support materials such as AlPO-34, SAPO-34, NaAPSO-34 and LaAPSO-34 in ODH catalysts. It was demonstrated that the cracking reactions were inhibited with the use of SAPO-34 catalysts. Thus, deactivation effects were practically absent, even during long times-on-stream in a laboratory scale reactor. Upon the introduction of active metals such as V, Co, Mg and Mn, the ALPO-5 supported catalysts showed improved activity. However, ethylene selectivity did not exceed 65% [L. Marchese, “Acid SAPO-34 Catalysts for Oxidative Dehydrogenation of Ethane,” J. Catal., vol. 208, no. 2, pp. 479-484, June 2002—incorporated herein by reference in its entirety]. There are some studies that dealt with the acidic and basic Y zeolites supported transition metal (Ni, Cu, and Fe) catalysts in ODH reactions [X. Lin, C. a. Hoel, W. M. H. Sachtler, K. R. Poeppelmeier, and E. Weitz, “Oxidative dehydrogenation (ODH) of ethane with O2 as oxidant on selected transition metal-loaded zeolites,” J. Catal., vol. 265, no. 1, pp. 54-62, July 2009—incorporated herein by reference in its entirety]. Among these catalysts, the nickel-based catalysts show better activity and selectivity. Based on the catalyst activity and ethylene selectivity on these metal-loaded Y zeolites, samples were ranked as Ni/Y-zeolite>Cu/Y-zeolite>Fe/Y-zeolite [Y. Schuurman, V. Ducarme, T. Chen, W. Li, C. Mirodatos, and G. A. Martin, “Low temperature oxidative dehydrogenation of ethane over catalysts based on group VIII metals,” Appl. Catal. A Gen., vol. 163, no. 1-2, pp. 227-235, December 1997—incorporated herein by reference in its entirety]. In order to improve the activity and selectivity of these catalysts Li, Mg, Al, Ga, Ti, Nb and Ta have been used as promoters [Y. Wu, J. Gao, Y. He, and T. Wu, “Preparation and characterization of Ni—Zr—O nanoparticles and its catalytic behavior for ethane oxidative dehydrogenation,” Appl. Surf. Sci., vol. 258, no. 11, pp. 4922-4928, March 2012; H. Zhu, S. Ould-Chikh, D. H. Anjum, M. Sun, G. Biausque, J.-M. Basset, and V. Caps, “Nb effect in the nickel oxide-catalyzed low-temperature oxidative dehydrogenation of ethane,” J. Catal., vol. 285, no. 1, pp. 292-303, January 2012—each incorporated herein by reference in its entirety].
Haddad and colleagues examined Mo-based catalysts having both V and phosphorous as promoters. These bimetallic catalysts were found to be effective, especially when both V and phosphorous were added together [N. Haddad, E. Bordes-Richard, L. Hilaire, and a. Barama, “Oxidative dehydrogenation of ethane to ethene on alumina-supported molybdenum-based catalysts modified by vanadium and phosphorus,” Catal. Today, vol. 126, no. 1-2, pp. 256-263, August 2007—incorporated herein by reference in its entirety]. Vanadium with Ti, Sn or Zr pyrophosphates supports were studied in an ODH reaction [L. Lisi, G. Ruoppolo, M. P. Casaletto, P. Galli, M. a. Massucci, P. Patrono, and F. Pinzari, “Vanadium-metal(IV)phosphates as catalysts for the oxidative dehydrogenation of ethane,” J. Mol. Catal. A Chem., vol. 232, no. 1-2, pp. 127-134, May 2005—incorporated herein by reference in its entirety]. Here, the catalyst exhibited a good conversion with selectivity up to 90%.
Cr-containing oxide pillared zirconium phosphate materials were synthesized using the fluoro-complex method which enhanced catalyst activity [B. Solsona, J. M. López-Nieto, M. Alcántara-Rodríguez, E. Rodríguez-Castellón, and a. Jiménez-López, “Oxidative dehydrogenation of ethane on Cr, mixed Al/Cr and mixed Ga/Cr oxide pillared zirconium phosphate materials,” J. Mol. Catal. A Chem., vol. 153, no. 1-2, pp. 199-207, March 2000—incorporated herein by reference in its entirety]. A multicomponent BaCl2—TiO2—SnO2 showed high selectivity of ethylene and low COx selectivity [Z. Wang, L. Chen, G. Zou, X. Luo, R. Gao, L. Chou, and X. Wang, “A novel BaCl2—TiO2—SnO2 catalyst for the oxidative dehydrogenation of ethane,” Catal. Commun., vol. 25, no. 3, pp. 45-49, August 2012—incorporated herein by reference in its entirety]. It was believed that the presence of Cl− ions in the catalyst played vital and positive roles in the ODH reaction. Although this catalyst displayed promising results (e.g. 92.6% ethylene selectivity), the observed deactivation rate was very high. The catalyst activity sharply declined during the initial time on stream.
Other types of metals have been tested for ODH including La, Nd, Sm and Gd. The synthesis of these catalysts was effected using a modified sol-gel method [Q. Zhou, D. Zhou, Y. Wu, and T. Wu, “Oxidative dehydrogenation of ethane over RE-NiO (RE=La, Nd, Sm, Gd) catalysts,” J. Rare Earths, vol. 31, no. 7, pp. 669-673, July 2013—incorporated herein by reference in its entirety]. Among these catalysts Gd—NiO displayed the best catalytic performance for the ODH reaction with 56% ethane conversion and 51% ethylene selectivity at 375° C. Cobalt-titanium (anatase) catalysts were also investigated alone and with addition of phosphorous [Y. Brik, “Titania-Supported Cobalt and Cobalt-Phosphorus Catalysts: Characterization and Performances in Ethane Oxidative Dehydrogenation,” J. Catal., vol. 202, no. 1, pp. 118-128, August 2001—incorporated herein by reference in its entirety]. It was shown in this respect that the addition of vanadium and phosphorous can enhance the ethane conversion, the ethylene selectivity and the catalyst stability and selectivity. This is the case despite the fact that Mo is more effective in the same aspects [N. Haddad, E. Bordes-Richard, and a. Barama, “MoOx-based catalysts for the oxidative dehydrogenation (ODH) of ethane to ethylene,” Catal. Today, vol. 142, no. 3-4, pp. 215-219, April 2009—incorporated herein by reference in its entirety].
Regarding mixed oxides, NiO—CeO2 has also been investigated. It has been shown that the addition of cerium oxide to NiO improves ODH catalyst performance [B. Solsona, J. M. López-Nieto, M. Alcántara-Rodríguez, E. Rodríguez-Castellón, and a. Jiménez-López, “Oxidative dehydrogenation of ethane on Cr, mixed Al/Cr and mixed Ga/Cr oxide pillared zirconium phosphate materials,” J. Mol. Catal. A Chem., vol. 153, no. 1-2, pp. 199-207, March 2000—incorporated herein by reference in its entirety]. V2O5/Nb2O5 catalysts with various V2O5 contents were also studied [A. Qiao, V. N. Kalevaru, J. Radnik, a. Srihari Kumar, N. Lingaiah, P. S. Sai Prasad, and a. Martin, “Oxidative dehydrogenation of ethane to ethylene over V2O5/Nb2O5 catalysts,” Catal. Commun., vol. 30, pp. 45-50, January 2013—incorporated herein by reference in its entirety]. This showed a 38% selectivity and 28% ethylene yield although pure Nb2O5 had very little activity by itself.
All of the above described studies were conducted in fixed reactors using air as an oxidizing source. This contributed to the COx formation due to complete oxidation of both the ethane fed and the ethylene product. Consequently, the ethylene selectivity was consistently low. Other drawbacks of the fixed bed ODH include catalyst deactivation as a result of coke formation, difficulty in separation of ODH products from the COx and accumulation of residual nitrogen when using air directly as the oxygen carrier.
It has been shown that combustion reactions can considerably be reduced by controlling the availability of gas phase oxygen. One of the possible alternatives is a gas phase, oxygen-free ODH in a circulating fluidized bed reactor, [S. Al-Ghamdi, M. Volpe, M. M. Hossain, and H. de Lasa, “VOx/c-Al2O3 catalyst for oxidative dehydrogenation of ethane to ethylene: Desorption kinetics and catalytic activity,” Appl. Catal. A Gen., vol. 450, pp. 120-130, January 2013; Bakare, I. A., Shamseldin M., Razzak, S. A., Al-Ghamdi, S., Hossain, M. M., de Lasa, H. I., Fluidized bed ODH of ethane to ethylene over VOx-MoOx/γ-Al2O3 catalyst: Desorption kinetics and catalytic activity, Chemical Engineering Journal, doi:10.1016/j.cej.2014.09.11—each incorporated herein by reference in its entirety]. Using this approach, the lattice oxygen is the one available for ODH. Once the catalyst is lattice oxygen depleted it can be transported and re-oxidized in a catalyst regenerator with a continuous air flow at a suitable temperature. It has been shown that up to 84.5% ethylene selectivity can be obtained in the temperature range of 550-600° C. Furthermore, the selectivity of the VOx based catalyst can be further improved with a MoOx modifications [Bakare, I. A., Shamseldin M., Razzak, S. A., Al-Ghamdi, S., Hossain, M. M., de Lasa, H. I., Fluidized bed ODH of ethane to ethylene over VOx-MoOx/γ-Al2O3 catalyst: Desorption kinetics and catalytic activity, Chemical Engineering Journal, doi:10.1016/j.cej.2014.09.11—incorporated herein by reference in its entirety]. It has been shown that MoOx enhances the reducibility of the VOx by preventing the formation of crystalline VOx phase and as a result ethane conversion is increased. Despite these valuable prospects, both the VOx and the VOx—MoOx catalysts show decreased ethylene selectivity above ˜600° C. The high reaction temperature favors complete oxidation of ethane/ethylene to COx in these catalysts.
Thus the selection of reaction temperature continues to be an issue in ODH. On one hand, one would like to operate the ODH reactor at the highest possible thermal level to achieve high ODH reaction rates. Reactor designers are striving to minimize reactor volumes by enhancing reaction rate. However, and from a practical view point, temperatures above 675° C. may favor thermal cracking of ethane (gas phase). Thus, one has to limit the ODH reaction temperature to 600° C. using a catalyst which display an appreciable reaction rate and give high ethylene selectivity [Bakare, I. A., Shamseldin M., Razzak, S. A., Al-Ghamdi, S., Hossain, M. M., de Lasa, H. I., Fluidized bed ODH of ethane to ethylene over VOx-MoOx/γ-Al2O3 catalyst: Desorption kinetics and catalytic activity, Chemical Engineering Journal, doi:10.1016/j.cej.2014.09.11—incorporated herein by reference in its entirety]. In addition, and if one consider the integrated ODH process having an ODH fluidized bed reactor and a fluidized catalyst regenerator, it appears the 600° C. thermal level provides a good compromise, eliminating the need of cooling and heating exchangers between the interconnected twin fluidized beds.
In light of the foregoing there remains an unmet need for solutions, such as catalysts, reactor design and reaction conditions, that effectively overcome the drawbacks of oxidative dehydrogenation reactions and improve their reactivity.